librarything and amazon are used to get social metadata rating/tags/reviews/series etc. from isbn. The other two are used to get basic metadata from title/author or isbn

Thanks for the added metadata sources.

Fortunately you have allowed us to disable plugins. I have chose to disable librarything for the same reason Starson17 wrote code to prevent the auto metadata download from overwriting Author and/or Title fields. I found this wonderful plugin overwriting my Series names and it bugged me.